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Abstract:

Described herein are various methods and devices for delivering
cryoablative therapy. One such device includes a cryoablation chamber and
a volume displacement chamber. In use, the volume displacement chamber
can be expanded to occupy a non-therapeutic volume.

Claims:

1-34. (canceled)

35. A cryotherapy catheter device comprising: an elongate catheter shaft
extending along a longitudinal axis between a proximal and distal end; an
expandable first chamber positioned proximate to the distal end of the
catheter shaft, the first chamber in fluid communication with a lumen for
transmitting cryofluid to the first chamber; a source of cryofluid that
is in fluid communication with the first chamber; an expandable second
chamber positioned proximate to the first chamber; a source of volume
displacement fluid in fluid communication with the second chamber,
wherein the first chamber is positioned transversely with respect to the
second chamber and wherein the second chamber is positioned to occupy a
non-therapeutic volume when expanded.

36. The device of claim 35, wherein, when expanded, the second chamber
and the volume displacement fluid are configured to insulate tissue from
the first expandable chamber and the cryofluid.

37. The device of claim 35, wherein at least a portion of the second
chamber extends longitudinally from the catheter shaft.

38. A cryotherapy catheter device comprising: an elongate catheter shaft
extending along a longitudinal axis between a proximal and distal end; an
expandable first chamber positioned proximate to the distal end of the
catheter shaft, the first chamber in fluid communication with a lumen for
transmitting cryofluid to the first chamber; a source of cryofluid that
is in fluid communication with the first chamber; an expandable second
chamber positioned proximate to the first chamber; a source of volume
displacement fluid in fluid communication with the second chamber,
wherein in the first chamber is positioned longitudinally with respect to
the second chamber and wherein the second chamber is positioned to occupy
a non-therapeutic volume when expanded.

39. The device of claim 38, wherein the first chamber is positioned
distally with respect to the second chamber.

40. The device of claim 38, wherein a wall positioned between the first
and second chambers insulates the volume displacement fluid from the
cryofluid when the first and second chambers are expanded.

41. The device of claim 40, wherein a distal wall of the first chamber
has a higher thermal conductivity than the wall.

42. A cryotherapy catheter device comprising: an elongate catheter shaft
extending between a proximal and distal end; an expandable volume
displacement chamber positioned proximate to the distal end of the
catheter shaft, the chamber in fluid communication with a source of
volume displacement fluid; multiple expandable cryochambers located
adjacent to the volume displacement chamber; and a source of cryofluid in
fluid communication with the multiple expandable cryochambers, wherein
the volume displacement chamber is configured to move at least some of
the multiple expandable cryochambers into position for delivering
croablative therapy when expanded.

43. The device of claim 42, where at least two of the multiple expandable
cryochambers are separated from one another by the expandable volume
displacement chamber when the volume displacement chamber is expanded.

44. The device of claim 42, where each expandable cryochamber
circumscribes the expandable volume displacement chamber.

[0002] Atrial fibrillation is a common cardiac arrhythmia. Patient's
suffering from atrial fibrilation experience malfunctions of their
heart's electrical system that cause the atria to quiver rapidly instead
of beating in a normal pattern. This quivering prevents the heart from
properly pumping blood and can eventually lead to clot formation and
stroke.

[0003] Treatments for atrial fibrillation include drug therapy,
electrocardioversion, and surgical or intravascular ablation techniques.
Surgical and catheter based techniques have grown in popularity because
drug therapy may be ineffective in some patients, showing success rates
as low as fifty percent. Along with this low success rate, drug therapies
also have deleterious side effects.

[0004] Surgical ablation requires a more invasive procedure whereby the
surgeon creates a maze-like pattern of incisions on the inside of the
patient's atria. The scarring that results acts to block the abnormal
electrical pathways in the heart that lead to atrial fibrillation.
Surgical ablation has a much higher success rate than drug therapies and
lacks the potential for side effects presented by drug treatment.
However, highly invasive (e.g., open-chest) procedures can present
substantial risks.

[0005] Catheter ablation techniques use a less invasive approach and
create scar tissue via a transvenous approach. A catheter delivers energy
or cools tissue to cause lesional scarring without cracking a patient's
chest.

[0006] While current treatments address atrial fibrillation, further
advances in ablation devices and their methods of use would be
beneficial.

SUMMARY

[0007] Described herein are methods and devices for providing cryoablative
therapy. In one aspect, a cryoablative device includes a cryoablation
chamber and a volume displacement chamber. In use, the volume
displacement chamber can occupy a non-therapeutic volume and reduce the
amount of cryofluid required to ablate target tissue.

[0008] In one embodiment, a cryotherapy catheter device comprises an
elongate catheter shaft extending between a proximal and distal end and
an expandable first chamber positioned proximate to the distal end of the
catheter shaft. The first chamber can be in fluid communication with a
source of cryofluid. An expandable second chamber can be positioned
adjacent to the first chamber such that expansion of the second chamber
applies pressure on the first chamber. A source of volume displacement
fluid can be in fluid communication with the second chamber.

[0009] In one embodiment, the first chamber is positioned to deliver
cryotherapy when filled with cryofluid. Conversely, the second chamber
can be configured to hold the first chamber in contact with tissue when
expanded. In one exemplary aspect, the expandable first chamber surrounds
at least a portion of the expandable second chamber. In another aspect,
the second chamber is completely enclosed by the first chamber. In yet
another aspect, the expandable second chamber is positioned at the
distal-most end of the catheter, and the expandable first chamber is
positioned distally of the second chamber.

[0010] In another embodiment, the first and second chambers share a common
wall. The wall can be adapted to insulate the volume displacement chamber
from the cryofluid chamber. For example, a wall positioned between the
first and second chambers can have a lower thermal conductivity than a
portion of an outer wall of the first chamber positioned for delivering
cryoablative therapy. In another aspect, at least a portion of a wall of
the first chamber can have a higher thermal conductivity than a wall of
the second chamber.

[0011] Further described herein is a cryoablation device having multiple
cryoablation chambers. The device can include an elongate catheter shaft
extending between a proximal and distal end and an expandable volume
displacement chamber positioned proximate to the distal end of the
catheter shaft. The volume displacement chamber can be in fluid
communication with a source of volume displacement fluid. The device can
further include multiple expandable cryochambers located adjacent to the
volume displacement chamber and a source of cryofluid in fluid
communication with the multiple expandable cryochambers. When expanded,
the volume displacement chamber is configured to move at least some of
the multiple expandable cryochambers into position for delivering
cryoablative therapy.

[0012] In another embodiment, a method of delivering croyablative therapy
is disclosed. In one aspect, the method includes the steps of providing a
catheter device comprising a catheter shaft, an expandable first chamber,
and an expandable second chamber. A user positions the catheter device
relative to target tissue such that the first expandable chamber is
positioned at least partially between the second expandable chamber and
target tissue. The first chamber is then expanded by delivering cryofluid
into the first expandable chamber and ablating tissue adjacent to the
first chamber. In addition, the second expandable chamber is expanded
with a volume displacement fluid.

[0013] It is to be understood that both the foregoing general description
and the following detailed description are exemplary and are not
restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings, which are incorporated in and constitute
a part of this specification, illustrate exemplary embodiments of the
invention and together with the description, serve to explain the
principles of the invention.

[0015] FIG. 1 is a side view of an exemplary embodiment of a cryoablation
device described herein.

[0016] FIG. 2 is a cross-sectional view of one embodiment of a
cryoablation device described herein.

[0017] FIG. 3 is a cross-sectional view of another embodiment of a
cryoablation device described herein.

[0018]FIG. 4a is a cross-sectional view of yet another embodiment of a
cryoablation device described herein.

[0019]FIG. 4b is a cross-sectional view of still another embodiment of a
cryoablation device described herein.

[0020]FIG. 5 is a cross-sectional view of another embodiment of a
cryoablation device described herein.

[0021]FIG. 6 is a cross-sectional view of another embodiment of the
device of FIG. 2.

DETAILED DESCRIPTION

[0022] Described herein are methods and devices for ablating tissue, and
in particular, for ablating tissue with a cryofluid. In one embodiment, a
cryotherapy catheter device is disclosed. The device can include an
expandable body comprising first and second expandable chambers that are
adapted to receive a cryofluid and a volume displacement fluid,
respectively. In one aspect, the first chamber is placed adjacent to
target tissue and cryofluid is delivered to effect ablation of the
tissue. The second chamber, spaced from the first chamber and target
tissue, can be expanded to increase the volume of the expandable body
and/or position the first chamber relative to the target tissue for
treatment of the target tissue. In one aspect, methods and devices are
adapted for cardiac cryoablation, and in yet another aspect, methods and
devices are disclosed for reducing the amount of cooling fluid necessary
to alter target cardiac tissue and block aberrant electrical signals.

[0023] FIG. 1 illustrates one exemplary embodiment of a system 10 for
ablating tissue with cryofluid comprising an ablation device 12 and a
source of fluid 14. In one aspect, device 12 includes an elongated body
extending between proximal and distal ends 16, 18. The distal end of
device 12 can include an expandable body 20 into which cryofluid can be
placed as will be discussed in more detail below.

[0024] Proximal to expandable body 20, device 12 can include shaft 22. In
one aspect, shaft 22 is defined by a flexible or rigid body having one or
more channels through which treatment fluids can be delivered. For
example, shaft 22 can include at least one lumen for the delivery of a
cryofluid and/or at least one lumen for the delivery of a volume
displacement fluid. In addition, wires for conducting therapeutic energy
and/or for sending/receiving sensed signals can extend along at least a
portion of shaft 22. In one aspect, the wires can communicate with
sensors positioned at the distal end of shaft 22 and/or on expandable
body 20.

[0025] The shaft can include a variety of features to facilitate insertion
and/or placement of the expandable body relative to target tissue. In one
embodiment, device 12 can include an articulating segment defined by a
portion of shaft 22. For example, a distal portion of shaft 22 can be
actuated by a user from a proximal location to steer expandable body into
a target location. In one exemplary aspect, shaft 22 can include push
and/or pull strands to transmit forces to the articulation segment.

[0026] The size and shape of shaft 22 can be chosen based on the intended
use of device 12. Where device 12 is used for cardiac ablation, shaft 22
can be sized and shaped for insertion through a vascular lumen. In
addition, the materials and structure of shaft 22 can be chosen to
provide a flexible elongated body. One skilled in the art will appreciate
that shaft 22 can represent the variety of catheter structures commonly
known in the art for a vascular approach. However, the devices described
herein need not be delivered via a transvenous route and/or the target
tissue need not be cardiac tissue.

[0027] The proximal end of device 12 can include a user interface or
handle 24 that permits a clinician to grasp device 12. Handle 24 can have
a variety of forms depending on the intended use of device 12 and/or the
environment in which device 12 is used. In one aspect, handle 24 can
include one or more sources of liquid or gas for expanding expandable
body 20. Controls for governing the delivery of liquid, such as a
cryofluid or volume displacement fluid, can, in one aspect, also be
located on handle 24. Alternatively, or additionally, handle 24 can be
configured to mate with one or more sources of liquid such as fluid
source 14. In one embodiment, source 14 includes a cryofluid and/or
volume displacement fluid and can further include a mechanism for
regulating and controlling expansion of expandable body 20 via delivery
of fluid.

[0028] Returning to expandable body 20, FIG. 2 is a cross-section of one
embodiment of a cryotherapy device in which expandable body 20 is defined
by a first and second chamber. First chamber 26 is configured to receive
cryofluid and second chamber 28 is adapted to receive a volume expansion
fluid. For example, first chamber can be in fluid communication with a
cryofluid source. In one aspect, a lumen extends from the proximal end of
device 12 to the cryofluid chamber (first chamber 26). The proximal end
of the lumen can include a fitting for mating with a source of cryofluid,
particularly, with a source of pressurized gas. Conversely, the volume
expansion chamber, second chamber 28, can be in fluid communication with
a source of volume displacement fluid.

[0029] In one aspect, first chamber 26 surrounds at least a portion of the
second chamber and/or is positioned adjacent to the exterior or outer
surface of second chamber 28. In use, the first chamber is located at
least partially between target tissue and the second chamber. The
relative location of the first and second chambers allow second chamber
28 to occupy a non-therapeutic volume of the expandable member such that
the amount of cryofluid delivered to expandable member 20 is reduced.
First chamber 26 can receive cooling fluid and cool target tissue
positioned proximate to the first chamber while second chamber 28 can be
expanded with a different fluid or higher temperature fluid (e.g., liquid
and/or gas).

[0030] When positioned within an anatomic structure, such as a vascular
structure, expansion of second chamber 28 can assist with positioning
and/or shaping first chamber 26. In a first aspect, second chamber 28 may
apply pressure against first chamber 26. In this aspect, filling second
chamber 28 with volume displacement fluid may act to move first chamber
26 towards or into contact with the target tissue. Additionally, or
alternatively it may cause first chamber 26 to adopt a shape that
partially conforms to that of the target tissue by pressing chamber 26
into the tissue. In another aspect, second chamber 28 may act as a base
from which first chamber 26 may expand. In this aspect, expanded second
chamber 28 occupies a non-therapeutic portion of expandable body 20, thus
partially defining the shape of first chamber 26 and placing a greater
portion of first chamber 26 closer to the target tissue.

[0031] Second chamber 28 can also assist with insulating non-target
tissue. In this aspect, second chamber 28 may comprise a portion or
portions of the outer surface of expandable body 20, thereby excluding
first chamber 26 from a portion or portions of the outer surface of
expandable body 20. Tissue adjacent to or in contact with first chamber
26 can receive cryotreatment by being located near the cryofluid
contained in first chamber 26. The tissue adjacent to or in contact with
second chamber 28 can be insulated from the cryofluid contained in first
chamber 26 by the fluid displacement fluid contained in second chamber
28, thereby avoiding cryotherapy treatment. Thus by locating second
chamber 28 adjacent to or in contact with sensitive tissue, such as
tissue not to be treated with cryotherapy or tissue previously treated
with cryotherapy, second chamber 28 can protect such sensitive tissue
through insulation.

[0032] In one embodiment, the first and second chambers are defined by
first and second members 30, 32, respectively. The first member 30
defines, at least in part, the boundary of first chamber 26, and second
member 32 defines, at least in part, the boundary of the second chamber
28. However, the first and second members need not exclusively define the
first and second chambers. For example, as illustrated in FIG. 2, the
second member 32 can define the inner surface of the first (outer)
chamber and the outer surface of second (inner) chamber 28. The first and
second members need not comprise a single contiguous material. For
example, the first and second chambers can be defined by one or more
walls having the same or different material properties. In addition, the
walls of the first and second chambers can include one or more layers.

[0033] Regardless, at least a portion of the first and second chambers are
expandable. In one aspect, first and second members 30, 32 can be
expanded or inflated by stretching. Alternatively, the first and/or
second member may be a non-stretchable, but flexible material. A member
so constructed could expand by unfolding from an original collapsed
and/or folded configuration. In another aspect, at least a portion of the
first and/or second member can be deformable. Expansion can be achieved
by deforming the walls of expandable member 20.

[0034] In one embodiment, outer member 30 and inner member 32 can have
different properties. For example, outer member 30 can have a higher
thermal conductivity relative to the inner member to facilitate heat
transfer between a cryofluid within the first chamber and adjacent target
tissue. Conversely, inner member 32 can have a lower thermal conductivity
to limit the amount of heat transfer to the cryofluid within the first
chamber and/or to inhibit freezing of the volume displacement fluid. A
difference in the thermal conductivity can be achieved by using different
materials, by using different material thicknesses, and/or by using an
insulative layer.

[0035] A variety of conventional cooling or cryofluids can be used with
the devices described herein. The coolant fluid used to fill the first
chamber 26 may be a liquid or a gas, or it may change phase from liquid
to gas as it travels from the lumen through the first chamber 26. For
example, the coolant may be a liquid with a low freezing point, such as
saline, liquid nitrogen or other known heat transfer fluid.
Alternatively, the coolant fluid may be a compressed fluid such as nitric
oxide or other known refrigerant that expands as it enters the cooling
chamber, thus decreasing the temperature of the first chamber 26 through
the Joule-Thompson effect. In such instance, both the aerodynamics of the
fluid's expansion and the final volume of the first chamber 26 after
expansion can affect the final temperature of the coolant fluid.

[0036] The fluid used to fill the second chamber 28 can also have a
cooling effect and/or can be chosen solely to occupy space and expand the
second chamber. In one aspect, the volume displacement fluid is a
biocompatible or medical grade fluid such as saline. In addition, the
fluid may contain a contrast agent to aid in visualizing the cryotherapy
device. In another aspect, the volume displacement fluid is chosen such
that the volume displacement fluid does not freeze during cryotherapy
treatment. One skilled in the art will appreciate that the volume
displacement fluid can be selected depending on a variety of factors
including the intended use of device 20, the configuration of the first
and second chambers, the chosen cryofluid (e.g., cyrofluid temperature),
the volume displacement fluid freezing temperature, and/or thermal
capacity.

[0037] In one embodiment, cryofluid travels through the second chamber to
reach the first chamber. FIG. 3 is a cross-section of one embodiment of a
cryotherapy device having within expandable body 20 first chamber 26,
second chamber 28 and a pathway 40 extending through the second chamber
28. In one aspect, the pathway extends from the catheter shaft 22 through
second chamber 28 and exits into the first chamber 26.

[0038] Pathway 40 can be linear, extending along the longitudinal axis of
expandable body 20 and exiting at the distal end of second chamber 28 as
shown in FIG. 3. Pathway 40 also may be curvilinear, exiting from second
chamber 28 into first chamber 26 at a location spaced from the
longitudinal axis of expandable body 20. In another aspect, pathway 40
may be branched, having multiple exit points along inner member 32 into
first chamber 26.

[0039] In use, routing pathway 40 through second chamber 28 can insulate
cryofluid within pathway 40 from sensitive tissue and/or avoid
inconsistent or localized cooling. Chamber 28 can space pathway 40 from
the outer walls of expandable member 20.

[0040] In addition, allowing cooling fluid to enter first chamber 26 at a
distance from the proximal end of expandable body 20 can provide more
uniform cooling and/or can focus cooling at the distal end of expandable
member 20. With respect to FIG. 3, cooling fluid exiting pathway 40 is
directed toward first member 30 which direct the cooling fluid along the
inner wall of first member 30. As a result, the fluid travels along the
wall of the first chamber and mix with fluid within chamber 26. If
cryofluid enters chamber 26 immediately adjacent to the proximal end of
expandable member 20, the cooling may be concentrated at the proximal end
of the expandable member and/or may not mix efficiently. Thus, the size
and shape of pathway 40 and the location of its opening into first
chamber 26 can be chosen to improve the fluid dynamics and aerodynamics
associated with the expansion of the cooling fluid into first chamber 26.

[0041] In one aspect, an opening 41 of pathway 40 into chamber 26 is
spaced from the proximal end of chamber 26 and/or from the proximal end
of expandable member 20. In another aspect, opening 41 is closer to the
distal end of chamber 26 and/or expandable member 20 than the proximal
end of chamber 26 and/or expandable member 20. In yet another aspect,
opening 41 is positioned proximate to a longitudinal axis of expandable
member 20.

[0042] In one aspect, pathway 40 is defined by a lumen extending through
the second chamber and spaced from the sides of expandable body 20. The
wall 42 of the pathway can be defined by a portion of the second member
32 and/or a separate structure extending within the second member. In one
aspect, wall 42 can have a low thermal conductivity to insulate the
cryofluid from second chamber 28.

[0043] In another embodiment of the invention, a portion of each chamber
of expandable body 20 can be positioned adjacent to the outer surface of
expandable body 20 and/or partially define the outer surface of
expandable body 20. FIGS. 4A and 4B show cross sections of a cryotherapy
device having first chamber 26 and second chamber 28 within expandable
body 20 where a portion of each chamber partially defines the outer
surface of expandable body 20. In this aspect the first and second
chambers 26, 28 have a side-by-side configuration rather than an
inside/outside configuration as illustrated in FIGS. 2 and 3. In FIG. 4a,
the second chamber is located proximate to the distal end of catheter 22,
while first chamber 26 is located adjacent to the exterior or outer
surface of second chamber 28. In FIG. 4b, the first and second chambers
extend parallel to one another.

[0044] In one aspect, the first and second chamber are delineated by a
wall 50 that extends along a transverse (FIG. 4a) or longitudinal (FIG.
4B) plane. Wall 50 can be positioned along any plane through expandable
body 20 which allows the first chamber 26 to be placed in close proximity
to tissue to be treated. Further, wall 50 need not be planar. For
example, first chamber 26 may curve around a portion of second chamber
28, creating a non-planar wall 50.

[0045] In addition to requiring less cooling fluid than a single chamber
device, devices like those described in FIGS. 4A and 4B allow for full
expansion of expandable body 20 while limiting treatment to only a
portion of the tissue on the interior surface of a chosen anatomic
region. It may be desirable to treat only the tissue at the distal end of
expandable body 20, in which case a device such as the one depicted in
FIG. 4b can provide treatment. When it is desired to treat less than the
full circumference of tissue surrounding expandable body 20, a device
similar to the one shown in FIG. 4b would be useful.

[0046] Selective treatment of only a portion of the tissue can be achieved
by designing the proper shape of first chamber 26, designing a
complimentary shape for second chamber 28, and placing expandable body 20
into the anatomic feature such that first chamber 26 is only adjacent to
or in contact with tissue to be treated.

[0047] First chamber 26 and second chamber 28 may be the same size or they
may each be different in size. Similarly the shape of first chamber 26
may be the same or different than the shape of second chamber 28.
Chambers 26 and 28 may have shapes corresponding to the anatomic
structure into which expandable body 20 is positioned. For example,
chambers 26 and 28 may have a cylindrical, spherical, conical or
irregular shape. For example, chambers 26 and 28 may have shapes adapted
to expand against the interior walls of the cardiac vasculature. In
another aspect, flexible and/or deformable walls of device 12 allow the
expandable member to adapted to the surface features of the target
anatomic structure.

[0048]FIG. 5 illustrates another embodiment of a cryotherapy device
having an expandable volume displacement chamber 28 and multiple cooling
chambers 62a-c located within expandable body 20. In one aspect, the
multiple cooling chambers 62a-c are positioned adjacent to the exterior
or outer surface of the expandable volume displacement chamber 28 and in
closer proximity to target tissue. Conversely, second chamber 28 can be
located centrally and configured to occupy a non-theraputic volume. In
use, the volume displacement chamber (chamber 28) can be expanded to move
the cooling chambers into contact with tissue and/or to hold the cooling
chambers in contact with tissue.

[0049] Such a device allows for the treatment of non-contiguous regions of
tissue. For example, the arrangement of multiple cooling chambers 62a-c
depicted in FIG. 5 allows for alternating circumferential bands of
treated tissue and circumferential bands of untreated tissue. Other
patterns of treated and untreated tissue are possible by adapting the
location, size and shape of the multiple cooling chambers 62 to form the
desired treatment pattern.

[0050] In one embodiment, an outer member 64 defines, in part, a boundary
of multiple cooling chambers 62 and the outer boundary of expandable body
20. In addition, inner member 32 defines, at least in part, the inner
boundary of the multiple cooling chambers 62a-c. In addition, inner
member 32 can define the outer boundary of the volume displacement
chamber 28. Outer member 64 and inner member 32 can each be expandable.

[0051] In another embodiment, each of the individual multiple cooling
chambers 62a-c are defined, at least in part, by separate expandable
members. In one aspect, inner member 32 may define, in part, the inner
boundary of the multiple cooling chambers 62a-c and outer member 64 may
be comprised of separate expandable members mated to inner member 32. In
this aspect, inner member 32 can also define the outer boundary of the
volume displacement chamber 28 and portions of the outer boundary of
expandable body 20.

[0052] Further described is an expandable body 20 with a protective outer
layer. In any of the embodiments described herein, an additional
expandable body can surround the first and/or second chambers. In one
aspect, the outer layer can space the cryoablation chamber from target
tissue to control or limit the amount of heat removed and/or the depth of
ablation. For example, FIG. 6 illustrates outermost chamber 29 positioned
in a surrounding relationship to first and second chambers 26, 28. The
outermost chamber can receive a source of volume displacement fluid that
occupies an area between a surface of the first chamber 26 and target
tissue. In addition, or alternatively, the walls of chamber 29 can
provide an additional layer of protection should one of the chambers
rupture or break.

[0053] In one aspect, device 12 can incorporate or communicate with
systems or devices for cardiac mapping. For example, expandable body 20
can incorporate sensors for sensing cardiac signals in adjacent tissue.
Such sensors can be positioned on the outer surface of the expandable
body and/or within (or inside) an outer layer of device 12 that permits
sensing therethrough.

[0054] Further described herein are methods of delivering cryoablative
therapy. In one embodiment, expandable body 20 can be positioned adjacent
to target tissue such as, for example, cardiac tissue. Once in position,
the first and second chambers can be filled (or partially filled, or
further filled) to position the cooling chamber in position for delivery
cryoablative therapy. In one aspect, cryofluid is delivered to the first
chamber. For example, cryofluid can flow from a fluid source through
catheter 22 and into the first chamber. A user or controller can regulate
the delivery of cryofluid and/or volume displacement fluid to achieve the
desired expansion. Alternatively, the expandable body 20 can be
constrained to limit the maximum expansion of the first and/or second
chambers.

[0055] In one aspect, the expandable body 20 can be partially expanded by
filling the second chamber 28 with fluid. Expandable body 20 can then be
further expanded by filling the first chamber 26 with cooling fluid. In
one aspect, first chamber 26 is expanded until expandable body 20 is in
intimate contact with tissue to be treated. Expandable body 20 may remain
in this expanded state for the time period required to ablate the tissue
adjacent to the first chamber 26. Following this treatment period,
cooling fluid can be removed from first chamber 26, and volume
displacement fluid can be removed from second chamber 28.

[0056] Alternatively, after placement of expandable body 20 near the
tissue to be treated, expandable body 20 can be partially expanded by
first filling the first chamber 26 with cooling fluid. After filling the
first chamber 26 with the desired amount of cooling fluid, expandable
body 20 can be expanded in order to place the first chamber 26 adjacent
to the tissue to be treated by filling the second chamber 28 with fluid.
Expandable body 20 can remain in this expanded state for the time period
required to ablate the tissue adjacent to the first chamber 26. Following
the treatment period, cooling fluid can be removed from first chamber 26
and volume displacement fluid can be removed from second chamber 28.

[0057] A third method of using system 10 involves locating expandable body
20 near the tissue to be treated and first expanding expandable body 20
by filling the second chamber 28 with fluid until the second chamber 28
is adjacent to the tissue to be treated. At this point second chamber 28
accounts for most of the volume of expandable body 20. Next, cooling
fluid is added to the first chamber 26 while at the same time fluid is
removed from the second chamber 28 such that the overall volume of
expandable body 20 remains substantially unchanged. This allows the first
chamber 26 to expand into the region adjacent to the tissue to be treated
and causes the second chamber 28 to be partially displaced away from the
tissue to be treated. Following the treatment period the cooling fluid
can be removed from the first chamber 26 and the fluid can be removed
from the second chamber 28.

[0058] Other embodiments will be apparent to those skilled in the art from
consideration of the specification and the disclosure therein. It is
intended that the specification and examples be considered as exemplary
only, with a true scope and spirit of the invention being indicated by
the following claims.